Abstract
We describe here a synthesis of the morphine partial structures 28 and 36, and of their enantiomers, which uses 7‐methoxy‐benzofurancarboxylic acid as starting material. A key intermediate in this scheme is compound 15, which is converted, via 1,2‐ketone shift, into 22. This latter is stereospecifically reduced to the alcohol 24 and converted to the amide 25. The diastereomer of 25 is afforded by stereospecific introduction of a ethoxycarbonyl group in 15 to yield the β‐ketoester 31, followed by Curtius degradation of the acid 32 to the acylamine 34.An efficient method for removal of the methoxy group in methoxy‐dihydro‐benzofurans is presented (Scheme 9), as is the functionalization of the N‐atom in 27 with concurrent complex formation between the free hydroxy group and boric‐acid. The aromatization of the furan ring (Scheme 10) with DDQ gave the expected benzofuran derivative 30.
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